A jointer is a machine used in the woodworking field to square, that is, make the edge of a board straight and make it perpendicular to the board upper or lower surface. A typical jointer is a specialized machine that has a fence against which the board edge is pushed to interact with a group of knives rotating at high speed. A person who practices woodworking on a limited basis, such as a hobbyist, often does not own a dedicated jointer since the cost is not justified for its relatively limited use.
Such a casual woodworker has been provided an inexpensive substitute in a device called JOINT'R CLAMP KIT, that was invented and is now being sold by SIMP'L PRODUCTS of Mount Vernon, N.Y. This device, as shown in FIG. 1, is used with a common table saw that is owned by many casual woodworkers. This clamp kit accomplishes the task of squaring an edge E of a working board B. The kit includes a pair of specialized bi-level clamps 10 of the same construction that are used with a reference board R that has a straight edge RS. The clamp 10, which is an aluminum extrusion, has a base 12 that is to rest and slide on the table T of the saw. A plurality of spaced raised ribs 14 extend on the bottom of clamp base 12 in the direction of which it is to slide on the table T of the table saw to reduce sliding friction. A main wall 16 extends vertically upwardly from near the center of the upper surface of base 12. A lower clamp support wall 18 extends horizontally outwardly from and transverse to the base main wall 16 and an upper clamp support wall 20 extends outwardly from and transverse to the main wall 16 in the opposite direction to lower support wall 18. A threaded hole 18a and 20a is provided in each of the lower and upper support walls 18 and 20 to accept a respective thumbscrew 18b and 20b. 
The space between the base 12 upper surface and the lower surface of the lower support wall 18 forms a channel C1 in which one edge of the reference board opposite the reference straight edge RS is placed to engage the clamp main wall 16. The space between the base 12 upper surface and the under surface of the upper support wall 20 forms another channel C2 in which the edge of the board B opposite to the one being squared is placed to engage the clamp main wall 16. The main wall 16 also has ribs on both sides which the edges of the boards R and B engage. The edges of boards R and B that engage the main wall 16 do not have to be squared.
In the use of the kit, a rabbet 23 is made in the lower surface of the reference board R. The outer edge of the part of the base 12 that forms the channel C1 fits in the reference board rabbet 23. The rabbet 23 has a depth selected so that the lower ends of the clamp base ribs 14 and the lower surface of the reference board R will be in the same plane when sliding on the saw table T. One clamp 10 is placed near each end of the reference board R which is clamped in the channel C1 by tightening the thumbscrew 18b. One edge of the working board B is inserted into the channel C2 of each of the two clamps 10 to engage against their respective main walls 16. The working board B is secured in channel C2 by tightening the thumbscrews 20b of the two clamps. The edge of the working board B that is to be squared is remote from the main wall 16 of each clamp.
The channel C2 preferably is of greater height than the channel C1 so that the working board B can be thicker than the reference board R. But this is not absolutely necessary. The reference board R can be, for example, a 1″×3″ piece of stock lumber that has actual dimensions of ¾′×2¾″ and can be from 2 to 3 feet long. A reference board of any suitable dimensions can be used as long as the edge that is to ride against the table saw adjustable rip fence is squared. In a commercial version of the clamp 10 the height of the channel C1 is about 1″ and that of the channel C2 about 2.5″. The width of the lower support wall 18 extending horizontally from the vertical main wall 16 is about 1″, the width of the upper support wall 20 is about 1.5″ and that of the base 12 is about 3″. The length of the base is about 2.5″. These dimensions are not critical.
The table saw rip fence 27 is set to the desired distance from the saw blade 31 to determine the point in the working board B at which to make the squared edge. The straight edge RS of the reference board R is guided against the table saw rip fence 27 and the saw blade 31 makes the cut to form the edge E in the working board. The saw cut will produce a straight and squared edge E since the straight edge RS of the reference board is being guided against the table saw rip fence 27, which is a straight edge parallel to the rotating saw blade 31.
The jointer clamp set kit of FIG. 1 generally operates in a satisfactory manner. However, if the width of the working board B is much greater than the width of the portion of base 12 that forms the channel C2 on which a part of working board B rests, particularly when the working board is thick and/or heavy, the working board in the clamp channel C2 may tilt down slightly from the plane of the upper surface of the base 12. Therefore, when the saw blade 31 makes the cut to form the edge E in the working board, the cut might be slightly tilted relative to a true perpendicular from the surface T of the saw table and the surfaces of the working board. Therefore, the edge E cut by the saw blade 31 will not be truly square to the working board top surface. Accordingly, it is desirable to improve the clamp set of FIG. 1. to be able to overcome this problem.